1. Field of the Invention
The present invention relates to a variable nozzle opening control system for an exhaust turbine supercharger which is provided in an internal combustion engine, compresses intake air, and supplies the compresses intake air to the internal combustion engine.
2. Description of Related Art
There has been known an exhaust turbine supercharger as a device for supercharging intake air to an internal combustion engine. The exhaust turbine supercharger comprises a turbine provided in an exhaust gas conduit of an internal combustion engine and a compressor provided in an intake air conduit, drives the exhaust turbine with an exhaust gas from the internal combustion engine, and compresses the intake air by driving the compressor with this driving force.
In some of the exhaust turbine supercharqers, an opening of a nozzle section of the exhaust turbine is variable so that a supercharging pressure can be controlled. In this type of exhaust turbine supercharger, a movable nozzle vane is provided in the nozzle section which is a section for introducing an exhaust gas from the exhaust turbine, and an opening of the nozzle section is controlled by moving this nuzzle vane. When the nozzle vane is throttled to reduce the opening of the nozzle section, a flow rate of the exhaust gas introduced into the exhaust turbine becomes higher and the energy received by the exhaust turbine increases, so that the supercharging pressure can be raised. The nozzle vane is generally controlled according to the load, and for instance, the inlet port pressure (exhaust pressure) is compared to the outlet port pressure (boost pressure), and the nozzle vane is opened or closed according to the difference (or the ratio).
In control of a nozzle vane for an exhaust turbine supercharger used in a diesel engine for a truck or a bus, an opening of the nozzle vane is minimized in the low load mode. However, when the opening of the nozzle section is made smaller in the low load mode, a flow rate of the air flowing into the internal combustion engine becomes higher, and the air intake resistance increases, so that the pumping loss in the diesel engine becomes larger, so that the fuel consumption rate disadvantageously increases.
On the other hand, as described in Japanese Patent Laid-Open Publication No. 63-5117, when the opening of the nozzle vane is maximized in the low load mode, although the pumping loss is suppressed, there occurs the problem that responses of the nozzle vane to the transitional situation associating changes in load or speed become slower. Especially when the exhaust turbine supercharger is used, for instance, in a diesel engine for a construction machine, the load largely changes, and deceleration and re-acceleration are frequently repeated, so that improvement in response speed in the transitional situation is very important.
It is an object of the present invention to provide a variable nozzle opening control system for an exhaust turbine supercharger with a low fuel consumption rate in the low load mode and a high response speed in the transitional situation.
The variable nozzle opening control system according to the present invention comprises a nozzle opening adjuster capable of adjusting an opening of a variable nozzle for an exhaust turbine supercharger, a load detector for detecting a load of an internal combustion engine to which the exhaust turbine supercharger is connected, and a control unit for controlling operations of the nozzle-opening adjuster, and the control unit is previously set so that an opening of the variable nozzle is substantially maximized when the internal combustion engine runs in the low load region and also the opening of the variable nozzle is gradually reduced in association with increase in the load when the internal combustion engine runs in the high load region where the load of the internal combustion engine is higher than a preset level, and also so that, after the load of the internal combustion engine shifts from the high load region to the low load region, an opening of the variable nozzle for the original high load region is preserved or reduced for a first prespecified period of time and then set to a preset value after the first prespecified period of time has passed.
With the present invention based on the configuration as described above, an opening of a variable nozzle is controlled in the so-called constant operation mode of an internal combustion engine, in which no change occurs in load of the internal combustion engine, so that it is substantially maximized in the low load region and gradually made smaller in association with increase of the load when the load is not less than a first preset load level, and because of this configuration, the optical supercharging pressure can be maintained in various operation modes. Especially, in the low load region, pumping loss in the internal combustion engine is reduced with the fuel consumption rate reduced.
When shifting from the high load region to the low load region, as an opening of the variable nozzle is maintained at the original value in the high load region or at a smaller opening as compared to the original value for a first prespecified period of times even if a high load is reloaded during this first prespecified period of time, the supercharging pressure is maintained at a high level, so that the response speed in the transitional situation is quite excellent. The present invention is useful especially when it is used in a diesel engine for a construction machine or the like in which load change occurs frequently.
A variable range of an opening of a variable nozzle is decided by taking into considerations such factors as the performance of an exhaust turbine supercharger or an internal combustion engine. Therefore, the gate area of the nozzle section when the variable nozzle is fully opened or fully closed is decided according to a range in which an opening of the variable nozzle is variable.
The prespecified load is employed when the supercharging pressure is required to be raised, and is previously decided taking into considerations, a range in which the opening of the variable nozzle is variable, a range of the performance of an exhaust turbine superchargers or an allowable operating range of the internal combustion engine.
In the present invention, it is preferable to provide a rotation speed detector for detecting a rotation speed of an internal combustion engine, and the control unit preferably controls preferably provide controls so that, when the load of the internal combustion engine shifts from the high load region to the low load region, or when the rotation speed of the internal combustion engine shifts from the high speed side to the low speed side, the opening of the variable nozzle is enlarged for a second prespecified period of time, or until the rotation speed of the internal combustion engine drops to a first prespecified rotation speed, or until the load of the internal combustion engine drops to a second prespecified load level.
When the load of an internal combustion engine shifts from the high load region to the low load region, or when the load of an internal combustion engine shifts from the high speed side to the low speed side, if an opening of a variable nozzle of the exhaust turbine supercharger is kept as it is, or is changed to a smaller side, sometimes the operating region of the compressor may get closer to exceed the surging limit in some shift patterns of the load or speed. When the operating region of the compressor exceed the surging limit, vibrations of the exhaust turbine supercharger or noises due to the vibrations become larger, and in that case operations of the exhaust turbine supercharger may become unstable.
In the present invention based on the configuration as described above, when the exhaust turbine supercharger is used under the conditions where the situation as described above may occur, the control unit provides controls so that an opening of the variable nozzle is made larger, immediately after the load of the internal combustion engine is shifted from the high load region to the low load region or from the high speed side to the low speed side, for the second prespecified period of time, or until the rotation speed of the internal combustion engine drops to a first prespecified rotation speed, or until the load of the internal combustion engine drops to a second prespecified load level, so that the operating region of the compressor never reaches the surging limit during shift to the low load region side or to the low speed side, which insures stable operation.
In the present invention, the control unit preferably provides controls so that an opening of the variable nozzle is made larger within the first prespecified period of time, when the load of the internal combustion engine again shifts from the low load region to the high load region, or when the rotation speed of the internal combustion engine again shifts from the low speed side to the high speed side, for a third prespecified period of time, or until the rotation speed of the internal combustion engine reaches a second prespecified rotation speed, or until the load of the internal combustion engine reaches a third prespecified load level, and also so that, after the third prespecified period of time has passes, or after the second prespecified rotation speed is reached, or after the load of the internal combustion engine has reached the third prespecified load level, the opening is set to a preset value.
In diesel engines or the like for construction machines, it often occurs that the load of an internal combustion engine is shifted from the high load region to the low load region, or from the high speed side to the low speed side, and immediately after that the operating mode is again shifted to the high load region or to the high speed side. In this step, if an opening of the variable nozzle is kept at the original value for high load or high speed operation, an opening of the nozzle section of the exhaust turbine supercharger is smaller as compared to that required for actual operations and the back pressure of the internal combustion engine excessively rises. In this case, efficiency of the exhaust turbine substantially drops, or combustion is not performed smoothly because the exhaust gas is not discharged well.
In the present invention based on the configuration described above, when the operating mode of an internal combustion engine again shift to the high load mode or to the high speed region within the first prespecified period of time, the control unit provides controls so that an opening of a variable nozzle is made larger for the prespecified period of time, or until the rotation speed of the internal combustion engine reaches the second prespecified rotation speed, or until the load of the internal combustion engine reaches the third prespecified load level, and therefore abnormal increase of the back pressure is prevented, so that combustion is carried out smoothly and the response speed in the transitional situation is improved.
In the present invention, the control unit preferably provides controls so that an opening of a variable nozzle is made larger, when the load of the internal combustion engine again shifts from the low load mode to the high load mode or the rotation speed of the internal combustion engine again shifts from the low speed region to the high speed region within the first prespecified period of time, for the third prespecified period of time, or until the rotation speed of the internal combustion engine reaches the second prespecified rotation speed, or until the load of the internal combustion engine reaches the third prespecified load, and also so that, after the third prespecified period of time has passed, or after the second prespecified rotation speed is reached, or after the third prespecified load is reached, the opening of the variable nozzle is made smaller for a fourth prespecified period of time, or until the third prespecified rotation speed is reached, or until a fourth prespecified load is reached, and further so that, after the fourth prespecified period of time has passed, or after the third prespecified rotation speed is reached, or after the fourth prespecified load is reached, the opening is set to a prespecified value.
In the present invention based on this configuration, when the operating mode of the internal combustion engine again shifts from the high load mode or to the high speed region within the first prespecified period of time, an opening of a variable nozzle is made larger to prevent abnormal increase of the back pressure in the internal combustion engine for the third prespecified period of time, or until the rotation speed of the internal combustion engine reaches the second prespecified rotation speed, or until the load of the internal combustion engine reaches the third prespecified load, but then the opening is made smaller for the fourth prespecified period of time, or until the third rotation speed is reached, or until the fourth specified load is reached, and because of the operations, the supercharging pressure becomes higher, and the response speed in the transitional speed is further improved without causing abnormal increase of the back pressure.